The new research shows that stress also increases brain levels of a reproductive hormone named gonadotropin-inhibitory hormone, or GnIH, discovered nine years ago in birds and known to be present in humans and other mammals. This small protein hormone, a so-called RFamide-related peptide (RFRP), puts the brakes on reproduction by directly inhibiting GnRH.

The common thread appears to be the glucocorticoid stress hormones, which not only suppress GnRH but boost the suppressor GnIH – a double whammy for the reproductive system.

“We know stress affects the top-tier reproductive hormone, GnRH, but we show, in fact, that stress also affects another high-level hormone, GnIH, to cause reproductive dysfunction,” said lead author Elizabeth Kirby, a graduate student at UC Berkeley’s Helen Wills Neuroscience Institute. “This work provides a new target for researchers, a new way to think about infertility and dysfunction. The more we know, the more we can look for ways to treat it.”

The results will be published the week of June 15 in the Online Early Edition of the journal Proceedings of the National Academy of Sciences (PNAS)

The conclusions are based on experiments in rats and inferences from the effects of the hormone in birds. But if this new reproductive hormone acts the same way in all mammals, researchers say the finding could not only change the way physicians look at human reproductive problems, but also affect how breeders approach animal husbandry and captive breeding programs for endangered species.

“There is a growing body of work that points to GnIH as being a big player in the inhibition of reproduction in mammals,” said co-author George Bentley, UC Berkeley assistant professor of integrative biology. “We didn’t have any hint of this stress effect nine years ago, when GnIH was first discovered.”

In humans, chronic stress can lead to a drop in sex drive as well as a drop in fertility. Even the stress of infertility treatments can block their effectiveness, as evidenced by many anecdotes about couples conceiving children after the failure of assisted reproduction.

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Justin is a scholar and clinician of Classical Chinese Medicine living in San Diego, California, where he maintains a private practice specializing in stress, gastrointestinal, infertility, and autoimmune conditions.